Predator-prey behavioural interactions on plants, with special emphasis on aphid dropping defence and ladybird search strategies

Abstract

Predator-prey interactions have significant short- and long-term implications for the individuals involved, their populations’ dynamics, and the broader ecological community. Predation is a strong selective force that has led to prey evolving a great diversity of defensive adaptations, while predators undergo strong selection to successfully locate and capture prey. For both ‘sides’ of these interactions, behavioural adaptations offer flexibility in deployment, and so are expected to be context-sensitive. In this thesis, I use the ladybird-aphid predator-prey system to examine both prey defence behaviours and predator search strategies. Considering the prey, dropping – a widespread but understudied antipredator behaviour – is my focus. My findings suggest that, although dropping seems superficially simple, the selective pressures on it are complex. Dropping is affected by internal factors, such as genotype and the presence of endosymbionts. The nature and proximity of the predatory threat also affect dropping. Further, the consequences of dropping depend on many factors, including where on a plant predator-prey encounters occur; this in turn will be influenced by predator search strategies. Considering predator search, my focus is ladybird movements when searching branched environments, particularly potential turning biases and turn alternation. My work suggests that predators do not follow simple rules when searching a plant for prey, but they may exhibit some innate turning tendencies under particular conditions. Predator search strategies will be highly influential in affecting the context (e.g. location on plant) in which predator-prey interactions take place. Future work should investigate predator search further in order to provide a deeper understanding of the selective pressures on dropping in prey. For both prey dropping and predator search strategies, researchers must also appreciate the context-sensitivity of the different behaviours, and work to understand influencing cues, triggers, and outcomes specific to the species and circumstances involved.